The invention relates to a method of transmitting information from various sources over a common transmission means, and a multiplexing device for executing this method.
For transmission of digital information there are two different kinds of switching: circuit switching (line switching) and store-and-forward switching. In circuit switcing, previous to the transmission between two terminal stations a connection is established by signaling an information exchange which is then exclusively available and represents a "transparent" channel. Such connections are advantageous for continuous or synchronous traffic, but not for intermittent or interactive traffic. On the other hand, in store-and-forward switching no fixed connection is established. Data are formulated in blocks or "packets", transferred from node to node in a network, and intermediately stored at each node in a buffer. Additional data such as details on destination and source must be attached to the packets and associatively transferred and stored. Advantages of this kind of transmission are better line utilization and short response times. The transmitted data must, however, satisfy certain conditions (non-transparency) and one must put up with variable waiting times.
In communication systems for various information categories in which there are large variations in traffic volume, a combination of circuit switching and store-and-forward switcing, or of synchronous and asynchronous transmission is desirable. In principle, it would be possible to provide throughout the system parallel devices for both categories of transmission. This, however, is very expensive and does not give optimum utilization when there are large variations in the volume of traffic.